The creator of a video production or other image may set tones and colors of pixels in the image so that, when viewed, the image has a desired appearance which agrees with the creator's creative intent. For example, a creator may wish some scenes to have a darker, more oppressive, feel than others. The creator may wish certain features depicted in a scene to stand out or to be less prominent. The creator may wish to have colors seem extra vivid in some scenes and more muted in others. Adjusting tones and colors of pixels in an image may include performing color grading (or ‘color timing’) on the source video data. Color grading may be performed using a hardware/software system (sometimes referred to as a color grading station) that permits a user to change the video data in various ways to achieve a desired appearance. Color grading may involve manual user input (e.g., in the case of pre-recorded films or television programs) or be performed automatically according to pre-determined parameters (e.g., in the case of live broadcasts).
Some displays have a three dimensional (3D) display mode in which the display is operable to display 3D image data. In 3D display mode, a 3D visual effect may be generated by operating the display to deliver a different image to each eye of the viewer. The left and right eye images represent different perspectives of the same scene or object. The viewer's brain combines and interprets the left and right eye images to perceive a single 3D image having the illusion of depth. Such displays may be referred to as stereoscopic 3D displays. 3D image data, such as stereoscopic 3D video streams, for example, provided for display on such displays may be referred to as stereoscopic 3D content.
Various display technologies exist for delivering different images to the left and right eyes of the viewer. For example, in active 3D viewing technologies, the viewer may wear eyeglasses including optical shutters that are operated in synchronization with the display to allow only one eye to view the display at a time. The display is operated to show an image for viewing by the viewer's left eye while the left eye shutter is opened and the right eye shutter is closed. Then the left eye shutter is closed and the right eye shutter is opened while the display is operated to display an image for viewing by the viewer's right eye. The switches occur quickly enough that they are not perceptible to the viewer.
In other technologies, such as passive viewing technologies, the viewer may wear spectral filtration eyeglasses to view different left and right eye images. The display is operated to provide spectrally filtered light to the viewer so that the left eye is presented with light in a first set of spectral bands (providing a left eye image) and the right eye is presented with light in a complementary, second set of spectral bands (providing a right eye image).
In other passive viewing technologies, the viewer may wear polarized eyeglasses having polarizing filters (e.g. linearly polarized eyeglasses or circularly polarized eyeglasses). Images for viewing by the viewer's left and right eyes are each polarized so that they can be seen by the intended eye but not the other eye when wearing the polarized eyeglasses.
In addition to the above-noted technologies, other technologies exist for delivering different images to each eye to provide a 3D viewing experience. A non-limiting example of such a technology is autosteroscopic (or multi-view) displays.
Stereoscopic 3D content is often generated from paired content captured by distinct cameras having different viewpoints (e.g., left and right). Because grading multiple video streams is time consuming, expensive and/or fatiguing for a colorist (especially if done simultaneously), color grading of stereoscopic 3D video content is typically performed for only one video stream (the reference view video stream) and the same color grading operations applied to the other stream. Where there exist differences in exposure between the reference view stream and non-reference view stream, or of settings, lenses, and/or position of the cameras used to acquire the streams, this technique may result in mismatches between color and/or luminance characteristics among the streams. This may cause fatigue or eye strain to some viewers, and may result in a degraded image quality to others.
There is a need for methods and apparatus that provide efficient color grading of stereoscopic 3D content. There is need for methods and apparatus that provide color graded stereoscopic 3D content with improved color and/or luminance consistency among content for different views.
Literature in the general field of the invention includes:    US2011/0037829;    U.S. Pat. No. 6,111,596; and    Yibin Chen, Kai-Kuang Ma and Canhui Cai, Histogram-offset-based color correction for multi-view video coding, Proceedings of 2010 IEEE 17th International Conference on Image Processing, Hong Kong, Sep. 26-29, 2010.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.